In view of threats posed by criminals and terrorists, there is an ever-increasing need for systems aiming to detect the presence of intruders in protected areas.
U.S. Pat. No. 6,188,319 discloses a system for detecting the presence of an intruder in a protected area. A light beam is reflected from a target, which is a potential intruder. The system analyzes the measurements of distance and intensity of the reflected light. The algorithm for detecting the presence of an intruder is based on changes in the measured distance and/or intensity of reflected light, when compared to measurements performed during a previous background “learning” period of the area to be protected. The system utilizes a simple pulse detector in the laser range finder, but an intruder may attempt to defeat the system by moving in proximity of a background obstacle, by crawling on the ground or by walking close to a wall.
U.S. Pat. No. 6,842,231 to Nourrcier et al. discloses a laser range finder method using an Analog-to-Digital converter for sampling a portion of the reflected laser pulse. The complete shape and implicitly the center of the reflected pulse are being inferred by applying a delay function, calculating the slope of the reflected pulse once it crosses a threshold level and deducing the shape of the pulse by accessing a look-up table.
A scanning laser radar with adjustable operational parameters is disclosed by US Patent Application 2008/0278715 to Swenson et al. US Patent Application 2009/0091446 to Jang et al. reveals a security system using a laser range finder and a method for detecting an intruder by using a laser range finder.
The patents listed hereinabove seem not reveals systems or methods that detect an intruder which is very close to a background, and seem not perform repeated adjustments to an initial estimated distance up to a suspected point of intrusion, so as to decrease a likelihood of false alarm and increase precision of distance estimation.